2022 Mazda 6 not starting lost communication with pcm

Hi mate
yes this is the junction you mentioned before I removed the tape and the tupe covers the cables and the previous photos were from that area. 

see attached the photos again and attached how they were previously when you circled the junction in yellow. 

they looked okay to me
they in a big tube as shown but that tube looks fine not touched at all. 



 

You will need to trace the red and white lines from the tube that looks Ok to the ECM. There are other damaged areas in the wiring harness that I sent back. Look at the picture attached again. You will see 2 to 3 twisted pairs of red/white wires.

In the mean time, take the measurements below, from the the OBD port. You will need to find a way to access the port and see the pins. Unless there is enough space you will need an extension cable or ideally a breakout box to see what you are doing. Also, you may want to attach thinner test leads so they can reach the pin. Do not force them in. You can use something like needles, just make sure they are making good contact. See pic attached of the port/pins.

1.
PIN 16: battery voltage
PIN 4 and 5: ground
Make sure you are reading the pins’ numbers correctly.

2.
- Disconnect the battery and wait for at least a minute, then measure resistance between PIN 6 and 14. Reading should be between 58-62 Ohms. In your case, it will probably read 120 ohm because the ECM seems to be inaccessible, and presuming there is no short. You may get 0 ohms if wires are shorted. Unless they changed the design, Mazda has used the internal resistors in the ECM and Instrument Cluster.

- Disconnect the ECM (both connectors) and measure again. Did the readings change?

3.
- Reconnect the battery and turn the ignition on.
- Connect the multimeter to a good ground and connect the positive lead to the following pins:
* PIN 3: 2.5v ~ 2.6v
* PIN 11: 2.3v ~ 2.4v  

* PIN 6: 2.5v ~ 2.6v
* PIN 14: 2.3v ~ 2.4v

What were the readings?
 

One more thing, the communication wires I'm referring to go in and out of that junction connector. Can you confirm that's the case?

Hi mate 
I’ll do all that tomorrow just at work now , and ill
Update you , thank u heaps. 

thank u so much mate 
just one more question regarding the measurement ohms just change that in the multimeter right ? 

I’ll do that and take some photos 

Regarding the connectors I attached a photo 
it leads to nothing just a plug not sure it’s extra ..
I attached two photos 
one before and after removing the tape. 

Hi mate , hope you r well. 

the cables visually looks fine to me 

I did the reading sorry for too many photos 
But I have written on every photo what’s the reading for. I’ll post in two respond the photos not allowing me too many photos.  

im not sure what they mean 
but they seems to be fine .. 
please see attached and let know 

Photos … please see attached the remaining photos 

Thanks for sharing the readings!

This is interesting because the integrity of the network seems to be fine. When you disconnected the ABS, it did not make any difference because the terminating resistors are in the ECM and Instrument Cluster. We know the internal resistor in the ECM is working because the reading went up close to 120 ohms when disconnected. I can explain what these readings mean later. For now, let's shift the focus to that fast blinking security/anti-theft light. First, get a scanner, as you did before, and scan all modules, clear all codes, re-scan and post the codes.

1. Is the security light still blinking fast?
2. Are there 'lost communication' faults?
3. Were all modules scanned? Some scanners show the network topology and indicate whether a module exists and if it's inaccessible.
 

Make sure you maintain good battery charge while scanning

Yeah which is so confusing .. 
I posted a photo as well 
when I unplugged the abs the reading was still 60 

also I don’t think it’s anything to do with the anti theft as the guy who came out who tried to read the car was saying it’s blank pcm and he says it can’t not scan the car because it’s not communicating with the Ecu of the car. 

he had to  force entry where he typed the vin and typed the pcm number as when he type the vin it says after that the pcm is backed please manually type the pcm number. 

also I was watching many YouTube videos regarding this issue lost communications many seems it could be a shorted in one of the sensors that’s causing not communication to ecu but I’m not sure. 

When you unplugged the ABS and got 60 ohms, that’s normal, because the ABS does not have the resistor. The ECM does, which is why you got close to 120 when you unplugged the ECM.

If the anti-theft light is blinking like that, it will not start. Do not ignore that.

Before you go further with sensors that could be shorting the ECM, we know it’s alive because you can see the check engine light on when you turn the ignition on. So, first verify that there is/isn’t communication to it after you clear all codes and re-scan as I mentioned the previous post. Post back the result for 1 through 3 and will go from there.

 

Hi mate 

yea I saw a YouTube video explaining that 
which means the CAN bus and power is all good at the pcm .. 


and yes I attached a photo as well before when I reconnected abs was still reading 61. 


and for the scanner I tried to scan it as the other guy said it’s reading the car computer 
so it doesn’t scan 
please see attached d

it connects to the obd but keep asking to turn the ignition on. 

im still still thinking i it’s to do with a sensor that’s shorted and not sending ground to the pcm but I have no ideas how to check that. 
Or I might be wrong .. would it be a bad ecu ? 



 

Hi mate
finally it started , it was actually a fuse ( I think engine fuse or something) 15 fuse

I went back and tested the voltage of the fuses 
which they should have battery voltage 
but one weird one had one side 11.5 and the other 8 voltage ?? That’s why the professional and my self when we used the test light it was lighting up so we didn’t check the fuse. See attached the location of it for other people who might benefit from this. 

so I’ve learned a lot 
next time check the voltage of the fuses not just test light. As it was lighting up before and has 8 voltage one side and 11.5 the other side which is the battery voltage. 


I just want to say thank you so much for your time and help I really appreciate it. You been a great help and I’ve learned a lot from you. 
so thank you mate. 

Hi mate
The engine light still there 
I managed to clear it but still comes back 

I scanned again and still got these codes 
any chance what they could be ? 

I cleared code all went away then 
also I had the battery management on unplugged the battery then plugged back the engine light came on but battery management is gone. 

so I cleared the code it’s gone engine light and I started the car for now to leave it running. 
so I would think engine light would still be there after I turn off and turn on ? But when I clear the codes they go away and I start the car.  

thank you again 

Glad to hear it started. You mentioned that you checked the fuses and they were Ok

Those are engine/Ignition fuses. One thing to keep in mind is why they blew. It's likely they are used by something else that shorted them. Maybe something in the broken connectors/wires. It's worth looking into a diagram in order to tell what caused the short.

You're welcome by the way!

When the car is running, what lights and malfunctions besides the check engine lights are on?

Yeah I’m really glad 
I did with test light and they were working 
and the professional who came out checked them out and also said ok .. 
I checked today with multimeter and saw the voltage was different one side to the other of that fuse. 




I think it did when I unplugged the earth cables behind the fender and I tried to start the car without when I was replacing the susp and lower arm. 


after I cleared code and left it running for a while 
I don’t see anything on Dash apart from the blind spot which I know why cos mirror if off. 

I have this light flashing which looks like the washer bottle or am I mistaken  ?

That's the hood/bonnet light. Check out this link: owners-manual.mazda.com/gen/en/mazda6/ma...ntents/03060100.html
That may be for a different year, but there should be an actuator and sensors, as illustrated. It must be the one(s) on the right side where there is connector/wiring damage.

Hi 
no that’s sensor is fine 
and yeah I think I left the bonnet open 
but never seen this sign before 

I’ll start tomorrow and check again 

but the question is : why did the fuse has 11.5 v and one had 8.3v ?  That’s where the confusing was 
cos when u test with a test light they looked fine til tested with multimeter. 

Which fuse and does it have power all the time? If so, measure voltage when ignition is off, accessories on and when the engine is running. Are all 3 readings the same?
Also, the fuse reading 11.5v, was that battery voltage at the time?

Hi 
Now they are reading nothing with the car is off 

when car is on
they are all reading now 14.10. 

please see attached the fuse location 

also do you know why these left empty ? 


also can you help me with a diagram to what these cables next to my headlight cables ? 
I know one or two for washer bottle 
one for parking sensor 
one going to the intercooler 
there is one I don’t know if it’s extra for fog light or what exactly is it ( I attached a photo from previous )